1. Field of the Invention
The present invention relates to a calibration apparatus, a control method thereof, and an image display apparatus.
2. Description of the Related Art
A plurality of vertically-installed liquid crystal display apparatuses are sometimes arranged side by side to be used as medical liquid crystal display apparatuses. However, when liquid crystal display apparatuses are arranged side by side, the presence of centrally arranged bezels of the liquid crystal display apparatuses obstructs a field of view. Therefore, a large-size liquid crystal display apparatus that is twice as large is sometimes used. In addition, there are medical liquid crystal display apparatuses capable of dividing an image display region of the liquid crystal display apparatus into a plurality of regions and applying a different gradation curve or brightness to each region. Furthermore, there are medical liquid crystal display apparatuses which include a sensor for measuring brightness or chromaticity on the front of a peripheral part of a screen (hereinafter, front sensor) and which are capable of performing a quality management test or calibration of the liquid crystal display apparatus without using an externally-installed sensor which is provided separately from the liquid crystal display apparatus (hereinafter, external sensor).
However, since liquid crystal display apparatuses characteristically have greater color unevenness and brightness unevenness in a peripheral part than a central part of a screen, techniques are being proposed for associating a measurement value in the peripheral part as taken by a front sensor and a measurement value of the central part as taken by an external sensor. For example, Japanese Patent Application Laid-open No. 2007-34209 proposes storing a relative ratio of a central part and a peripheral part of a liquid crystal display apparatus in advance and, during calibration, converting brightness measured by a front sensor during calibration into brightness of the central part based on the relative ratio. In this case, brightness of the liquid crystal display apparatus is adjusted based on the brightness of the central part. In addition, for example, Japanese Patent Application Laid-open No. 2012-14004 proposes calculating a characteristic quantity of a central part of a screen based on a characteristic quantity of a peripheral part as measured by a front sensor and a correction value for correcting a gradation value of an input signal according to characteristics of display unevenness of the screen.